1. Field of the Invention
The invention relates to an adjustable-length gas spring, the adjusting valve of which can be opened and closed externally, with the piston rod, in the opened condition, can be retracted into, or extracted from, the casing, length adjustments of the gas spring thus being performed. With the adjusting valve closed, the gas spring is blocked in relation to the casing in this set position of the piston rod. In particular when the piston of the gas spring is movable in an interior chamber that is filled with hydraulic oil, the gas spring is rigidly blockable against compression forces.
2. Background Art
Quite a number of adjustable-length gas springs of the generic type have been known, which have additional functions such as an overload protection in which the adjusting valve opens when inadmissible high forces act between the piston rod and the casing.
When adjustable-length gas springs of the species—in particular rigidly blockable gas springs—as mentioned above—filled with hydraulic oil—are used in tables, pivoted head rests of hospital beds, hospital side tables etc., there is a desire for having an increase in length of the gas spring without any need of operation of the adjusting valve.